Molecular sieve catalysts have been used to convert oxygenate compounds to olefins. In this conversion process, a carbonaceous material, coke, is deposited on the catalyst. As the coke level builds, the catalyst deactivates. However, the catalyst can be reactivated by burning off the coke. This burning process is generally referred to as regeneration.
U.S. Pat. No. 4,873,390, Lewis, discloses a process for catalytically converting oxygenate to olefins. The process uses a molecular sieve catalyst that has been partially regenerated in order to increase the selectivity to desired olefin products. The preferred catalyst contains silicoaluminophosphate molecular sieve.
U.S. Pat. No. 6,023,005, Lattner, also discloses a process for catalytically converting oxygenate to olefins. This process, however, burns off most, if not all, of the coke deposit on the molecular sieve catalyst. In order to maintain a high selectivity to a desired olefin product, a relatively high average level of coke is maintained on the catalyst in the reactor. The desired level of coke on the catalyst is maintained by circulating a portion of the coked catalyst to the reactor without regenerating it. The regeneration process is shown to include a catalyst cooler.
Vora et al., “Conversion of Natural Gas to Ethylene and Propylene: UOP/HYDRO/MTO Process,” Chemical Engineering of Oil and Gas, Luzhou, Sichuan, China, July 1997, disclose a process for making olefins from methanol using a SAPO-34 based catalyst. Because of the high heat of reaction and the need to frequently regenerate the catalyst, the process uses a fluidized bed reactor and regenerator. The heat of reaction is removed by steam generation. Because of the fluidized bed conditions and well-mixed catalyst, the temperature in the reactor is almost isothermal. The spent catalyst is sent to the regenerator, where the coke is burned from the catalyst, Steam is generated in the regenerator to remove the exothermic heat resulting from coke burning.
As suggest by Vora et al., heat released during catalyst regeneration in the fluidized bed process of converting oxygenate to olefin is generally quite substantial, since a substantial amount of coke must be removed by reaction with oxygen before the catalyst is considered sufficiently regenerated for reuse. Typically, a means for heat removal (cooling) must be provided to prevent excessive regeneration temperatures, which requires relatively complex and costly equipment. It would, therefore, be highly beneficial to maintain the required degree of coke removal, yet sufficiently control catalyst temperature such that equipment for catalyst cooling could be eliminated. It is especially desirable to eliminate the need to use heat exchange equipment specifically for the purpose of catalyst cooling in the process of making olefin from oxygenate.